In the existing art, analysis of video images is commonly used as a means of detecting vehicles for providing information for actuation of traffic signals, and has been for many years. Cameras that capture these video images are typically mounted on fixed intersection infrastructure such as light standards, signal mast arms, wooden poles, etc. In video from cameras mounted in this way, a user draws detection “zones” of varying types onto an image using computing devices. These detection zones are drawn for each vehicle lane to determine the presence of vehicles, and are sometimes referred to as virtual loops as they perform a similar function to dedicated in-pavement road loops. These detection zones are also used in order to reduce the amount of the image that is required to be processed to allow existing commercially-available processing chips to be used.
While the method of mounting cameras on fixed poles works at many intersections, there is a class of intersections known as span wire for which this mounting location is problematic. Span wire intersections typically suspend wires across an intersection on which signal lights and other equipment for the motorist to see are mounted. Span wires typically comprise either single spans or a main span wire with a tether wire either above or below the wire to help stabilize equipment. The poles that these span wires are suspended from are often well away from the roadway and when video detection cameras are mounted thereon, they suffer from significant occlusion at least due to the angle to the roadway.
Cameras have been previously mounted on these types of wires spanning the intersection to obtain a better viewing angle, but when mounted in this way there is often significant camera motion which makes it difficult for video detection algorithms to accurately function. Most often, due to camera motion, vehicle detections are missed at a higher than desired rate and detections are made when no vehicles are present, known as a false call. This is because the detection zones do not move in sync with the image. Hence video detection algorithms do not work well in span wire implementations.
As a result, traffic management agencies using span-wire mounted signals have not previously been able to widely deploy video vehicle detection, as span-wire mounted cameras provided tough challenges for image processing algorithms, due to uncontrolled and random camera movement. Image stabilization systems exist in the prior art that can reduce the amount of movement in an image, and these have been applied to video streams to improve the actual image prior to entering the video detection algorithm. These systems, however, focus on the entire image, rather than implementing ways to stabilize a particular zone or area within an image instead of the image itself, and therefore are typically more expensive than desired, at least because they consume excessive computational capacity, rendering them slow and impractical in many situations.